Hydrocarbon-producing wells often are serviced by a variety of operations involving introducing a servicing fluid into a portion of a subterranean formation penetrated by a wellbore. Examples of such servicing operations include a fracturing operation, a hydra-jetting operation, a perforating operation, an acidizing operation, or the like. Such servicing operations may comprise the steps of positioning a work string within a wellbore penetrating the subterranean formation to be serviced and removing the work string from the wellbore after an operation or a portion of an operation has been completed.
Placement of the work string within the wellbore, often referred to as a “trip-in” or “run-in,” requires breaking and making multiple connections to the work string as the work string is lowered in the wellbore. For example, where the work string comprises jointed tubing, additional segments or tubing “joints” are incorporated within the working at the uppermost end of the work string as it is lowered into the wellbore. Therefore, each time an additional joint is to be added to the work string, the connection to the work string must be “broken” or disconnected such that the joint to be added may be inserted into the work string.
Similarly, removal of the work string from within the wellbore, often referred to as a “trip-out” or “run-out,” also requires breaking and making multiple connections to the work string as the work string is pulled out of the wellbore. For example, where the work string comprises jointed tubing, tubing joints incorporated within the work string are removed therefrom as the work string is pulled out of the wellbore. Therefore, each time a joint is to be removed from the work string, the connection to the work string must be broken and remade. Similarly, connections to a work string must be broken and made when using various other tubing configurations (e.g., coiled tubing).
Therefore, in either a trip-in or a trip-out, breaking a connection in the work string opens the work string and, because the work sting at least partially penetrates a wellbore which may be “live” (i.e., the wellbore may be under pressure), breaking the connection to the work string presents the possibility of backflow through the work string if the pressure within the work string is not isolated. Failure to isolate the wellbore pressure may allow fluid to escape from the work string presenting numerous complications including, among others, danger to workers, losses of time, and potential damage to equipment, and necessitating clean-up efforts.
Prior efforts to isolate the pressure of a work string have sometimes proven unreliable and, thus possibly unsafe. In addition, prior efforts to isolate the pressure within a work string have sometimes not allowed the operator the ability to isolate well pressure during trip-in, reverse-flow servicing fluids during a servicing operation, and isolate well pressure again during trip-out. Thus, there is a need for an improved means of isolating wellbore pressure.